The max allowable height is like all trucks determined by mast spec. Obviously when mast reaches top of stroke the pressure relief vavles prevent hydraulics from overloading.
Regarding lift height measurement there are several sensors and encoders on the free and main lift. There is an inductive sensor near the bottom about 800mm from bottom and another on the transition between free and main lift. I've looked into bypassing the measuring system on the RREs as they are very susceptible to problems where plastic can snare the encoders and/or damage the cables. It can be done but it takes a day or two. Having worked on most models I can't say I am impressed with the new Toyota models, not a patch on the 5 and 6 series Toyotas.

Probably should mention I discussed the lift height system with one of the Technical heads in Toyota and he agreed that bypassing the system was a tedious job. I've been providing technical support to Toyota for several years across Europe and they had numerous software problems which is reflected in the number of software patches released. They also had a major issue with TruckCom which required an emergency bug fix which was issued to their dealer network, so be careful which version of TruckCom you use. If you need further advice you can contact me by email for details.