Dahlias ... starting Indoors

I dig up my dahlias every year and replant in the spring.  After researching (internet) I had read about getting a "head start" indoors.  I placed them in 3" deep trays with potting soil, little moisture, and on heating pads.  Many are sprouting.   However, most of the WEB info that I found (the same that recommend 2-3" flat trays for starting) state to transplant outside at 6". 

Is it safe to bury the leafing sprouts ... to achieve the 6" depth?  BTW ... I grow mostly small Dahlhias (2' or less).