what kind of relation between thermal resistance and quality of power modules such as MTX300A etc ?

generally speaking , less and less thermal resistance value ,  the better quality about MTX module such as MTX300A  MTX600A MTX800A

the actual parameters of thermal resistance for MTX300A 600A 800A from our company are as following:

1)MTX300:   0.05 close to 0.04 with SKKH 250/16 E or SKKH 330/16 E

2)MTX600:   0.03 less than 0.036 with SKKH 430/16 E  ,cause we have bigger copper base with this kind of items ,so

we have better heat dissipation performance than Semikron items

3)MTX800:    0.027 a little more than  0.02 with SKKH 570/16 E