Don't you have different settings on your pad control? Just turn it down to the next setting as you go along.It seems to be working just fine as is...don't think any reflection is needed to increase the heat generated.
I'm actually concerned about being able to reduce the heat to harden them off for outside sooner rather than later.
Hoping that changing out the feet for long carriage bolts will get it high enough to lower the temp available to chicks, might have to restrict their access to the top.
Tho maybe that's not a concern with a plate instead of a lamp?