I may be in a unique position to help.
I run ST's on all my personal cars, and have been the wrench behind the @
LiftedBRZ project.
If you're trying run coilovers like the KW's where the bottom mount is fixed, and not what controls ride height, and aren't trying to actually lift it, just run the height at the upper end of KW's recommended ride height. You won't be compromising damper stroke much if at all, that's how KW designed them.
If you want to lower your car, while retaining as much stroke as possible, that's where the upper mount options come into play. Something like the Raceseng 1" or 2" upper mount will help you retain 1" or 2" respectively of stroke as you lower past the upper end of KW's recommended ride height.
I have my car dropped about 1.3" on ST's with stock top mounts all around, and haven't had any issues with bump stops or lack of stroke.
To properly setup these cars with as minimal of a drop as possible, measure hub to fender of your car stock, install and adjust until you have hub to fender - 20mm. That is the correct heighest setting for this coilover kit. These coilovers operating range is a 20-50mm drop. Towards the 50mm end you will experience a lack of stroke, (that's nearly a full 2" drop.)
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SOLD: 2015 WRB BRZ Limited ('02 WRX BBS, S-04's, Stoptech Sport pads, MXP SP, AVO drop in filter, Mishimoto Intake tube, decatted header, OFT 93 Stage 2 EL Tune, Kartboy rear shifter bushing, Whiteline transmission and subframe lockout bushings, ST Coilovers, SPC Camber bolts w/smaller crash bolt, SPC LCA's & SPC Toe Arm bushings, Red TOMs, TRD Wing.)