How about this idea to overcome laser intensity and focus problems, due to distance from print to peachy changing as the print progresses. Dump the upper tank completely and in the lower tank have a telescopic platform, say 8 inches in diameter and with nesting cylinders with a weight and an O ring. Place a valve at the base of the cylinder and open it as the print starts. the cylinders are full of saline and fully extended to contact the floating resin. When the valve is open, the weight pushes the top cylinder downwards and expels the saline into the tank, thru the orifice (so the level in the tank never varies). The platform will fall under gravity in an entirely deterministic way for a given orifice. So once calibrated, Z is deterministic. The cost of two nesting cylinders with an O ring is minimal and hence we could have a very cheap lowering platform, with a decent print size, and peachy would remain at a fixed distance from the print. This idea overcomes problems associated with floating solutions with the wobble factor and overcomes focus problems.