Thickness range

Yes. This is considered a single bevel, Tee-joint groove weld. If the 6mm plate was not beveled, this would be a square Tee joint, using a fillet weld.

Your welding procedure specification needs to be qualified for a 60mm base metal thickness included, and the corresponding groove weld deposit thickness.

I may be wrong but the grove in this case is 6mm and even if it is welded to a thicker plate, it only need qualifying for groove of 6mm and considet the thicker plate, also by welding to a thick plate may need supplementals as preheat on the thick plate.
BG

You might want to review QW 202.4. You will see that some additional information is necessary to correctly answer this question. If you have access to interpretations you might look at IX-95-12, & IX-98-20R. While these interpretations don't specifically address your question they do provide some general guidance.
If you still need some help, or don't have access to this info holler back.

arcer;
Correct. My response above was intended for base materials that were being joined as ferritic, in lieu of austenitic or non-ferrous. Per QW 202.4, if the dissimilar thickness material is NOT any of the following base metals; P-No 8, 41, 42, 43, 44, 45, 46,49,51,52,53,61, and 62

the base metal thickness of the weld coupon for weld procedure qualification must be 30mm, to qualify for a 60mm base metal thickness in production.

Otherwise, if the base metals being joined are either austenitic or non-ferrous, you only need to qualify on base metal 1/4" thick (minimum) or about 6.1 mm in thickness. The rationale being that austenitic and non-ferrous metals do not exhibit the same hardenability characteristics as ferritic steels, where thickness range must be qualified based on the need for weld preheat and post weld heat treatment.