What is cold lash?.
It is the space you leave between the lobe bacecircle and the lifter top when adjusting the valves. Valve adjustment of solid lifter motors is concidered normal maintenance should be performed periodically as the surfaces wear.
Metal expands when hot. An aluminum head will expand about .008". You have to account for the expansion by leaving the space between the lifter and the lobe. The lifters are adjustable for height through shims, they sit in the top of the lifter bucket and you can order different thicknesses. I have found the cold lash to be set at .015" front the factory and I recommend a closer tolerance of .008-010". This will lessen cold start lifter ticking and give ~.005-.007" more valve lift.
In addition to gaining extra lift by setting cold lash to minimum, some 99+ Miata SCCA showroom stock racers who did not set their cold lash had the shims pop out at high rpm because the extra lash gave the shim enough room to fly out.
Your shop manual explains the adjustment process and factory recommended specs. It is very tedious process.