Exige 350 tuning question

its an Exige 350 with supercharged 2gr-fe engine. oem came with tvs1320 supercharger but I've upgraded to tvs1900 plus ecu flash, making 400hp at crank. also added water methanol injection pre supercharger but after TB. I did not tune the ecu to work with water injection; its there to add bit of safety during summer track days, so at the moment it only spray at 200cc/min.

I was wondering if i could get more power by reduce pulley size from 90mm to 85mm (5.6%reduction) plus increase WM injection and tune it with lambda value. Car does not have intercooler, and tvs1900 is making 6.5psi at 4000 rpm, 8.7psi at 7000 rpm. (psi number were given by the tuner that sold me the tvs1900 kit)

with 5.6% pulley reduction, does that mean supercharger would be making 6.9psi @4000rpm and 9.2psi @7000rpm? (just add 5.6% to previous psi value?) car does not have boost sensor and I do not have access to the ECU, its encrypted.

it runs close loop at idle and low load; switch to open loop on higher load but i do not know when ecu is switching from close to open loop. is it possible to tune this type of setup by just looking at lambda value? it won't be the most efficient but will it make any gains from what I mention above?

there might be but i don't know any shop that i could trust to install standalone ecu here

any opinion would be appreciated, thanks!