During cloning, a very small light is perfect.
Now, have you tried hardening them off using an intermediate light before putting them under the HPS? For example, if you are cloning under a small CFL, try stepping up to a tube flouro shop light while they adjust to dry air and uptaking water through the roots rather than the stomata. When you see that they are in vigorous vertical growth, with a good respectable root system, put them under the HPS, but have it HIGH and lower it gradually, stopping if any wilt is observed.
A last trick is to use some type of anti-transpirant on them- LIGHTLY so as not to suffocate the lil things. Wilt-Pruf, neem oil, and SMC leaf wash are all possibilities. I like Wilt-Pruf DURING cloning and SMC AFTER, because it is a bit lighter weight than the plastic in wilt-pruf.
Just some hints to try out.