This is an interesting topic and one where we did extensive tuning work on turbocharged Doo's over the last 12 months, both on the dyno at MoTeC in Australia, on various race tracks this past winter and finally on the trail using pump gas.
Let me provide some basic information.
First, most people assume an engine is not under boost when the analog boost gauge shows 0psi at low load cruise speed. This is a false assumption. A typical NA engine will cruising at low load will usually show a MAP value of around 75kpa (vacuum)if the throttle is held steady and constant. The same engine fitted with a turbocharger and cruising at the same speed and load will show a higher MAP value of perhaps 95kpa (still vacuum). Anytime MAP value is below 100kpa, a typical analog boost gauge will not register any boost value. However, it has to be undertood that 95kpa is a very high load value for an ECU mapped for a naturally aspirated engine, actually it is basically a WOT MAP value.
What the above means is if the engine is indeed operated at low load and low speed but the MAP value reads above 90kpa..... then the oem ECU will interpret that condition as low speed & high load because the engine load channel is in fact the MAP channel as opposed to the throttle position channel. This is a 2 edge sword: on one hand, it will promote timing retard which is fine because you have more air mass being ingested into the engine..... but it will also increase the injector duty cycle beyond what is actually required because the ECU "thinks" the engine is highly loaded at low rpm, while in fact it is not at all.
Ok, so that is out of the way in terms of understanding that 0psi boost pressure on the gauge does not mean the engine is not getting additional air mass flow volume.
There was a comment made earlier about engine popping when running lean. Actually, this is more a function of the acceleration enrichement setting not being rich enough to allow for the rapid opening of the throttle body. The reality is the 1200 Doo has a high volume intake plenum that slows down the MAP signal. This is fine for the NA version of the engine, but in a forced induction application, the oem ECU does not have sufficient acceleration enrichement to account for the sudden manifold pressure rise when the throttle is quickly blipped and the turbo is already spinning quite fast. The oem ECU uses a TP based acceleration enrichement that should be further enriched to get ride of the occasional odd popping when accelerating quickly.... it does not matter how lean or rich the engine is setup to begin with, it has to do with rpm rate of change suddenly climbing up to a maximum value of around 12,000rpm per second and the fact the MAP signal is not fast enough to catch up with that sharp rpm rise which lasts only a few miliseconds and has a an acceleration and deceleration bell curve -- therefore TP is a better channel to tune fuel enrichement by anticipation of the fuel requirement rather than by sensor feedback.
Fuel calibration can not be optimized without a good understanding of ignition timing and fuel octane. While it is common knowledge that the 1200 turbocharged Doo will make best power at AFR's well above 12.3 -- this should only be attempted by people who understand what the proper ignition timing advance curve should be for any given boost level and fuel octane. When in doubt, it is obviously much safer to settle to a fat fuel setting around 11.5. When having no clue about what the ignition timing should be, then going for 10.5afr can be one option to move on the safe side but at the same time, it is a testimony the tuning is poor.
One other aspect that is often neglected after an injector change to higher flow units is the injection timing relative to the available 720* degrees injection time as well as the dead time calibration. Since most people are using the oem ECU, whenever the oem injectors are changed and/or modified.... the whole low duty cycle accuracy goes south and the engine becomes very difficult to tune for consistency at duty cycles below 30%. This is because modifying injectors changes the dead time values and these are locked into the oem Siemmens/VDO ECU and can not be altered. Matters become worst when replacing injectors as the oem ECU Dead Time tables relative to battery voltage does not and will never match the requirements of the new injectors. So the bottome line is you move into a situation where your engine no longer run as good as when it was totally stock. Again, when this happens... it is better to tune on the rich side to avoid lean issues as the whole system can not be predictable and repeatable anymore.
Ok, back to the topic... there is no reason why a properly tuned 1200 turbocharged Doo could not be very safely tuned to 14,2-14,4 low load cruise AFR, 13.6-13.9 normal cruise afr, 13.0-13,3 high load AFR and 12.3 WOT AFR. If in doubt about the timing curve versus the fuel octane and boost load..... then enrich one full point from the above figures. If you really do not know what you're doing and you're very concerned about your tune not being right, then enrich 2 full points.
The sad reality is the fact the oem ECU was never designed to support a forced induction to begin with. The timing curve is very inapropriate and there is no air charge temperature compensation to properly trim ignition timing and fuel. Air temperature getting into the engine in the NA version rarely exceeds 35F degrees.... Air tempereture getting into the engine on a turbo setup always exceeds 85F degrees.... that's a massive difference that throws ignition timing and fuel calibration off.
My $0.02 on the subject. I hope it provides a useful perspective.