Does the lighting fixture size change the number of allowed wires in a junction box?
Here is a Code language excerpt for your situation:

314.16(B) Box Fill Calculations. The volumes in paragraphs 314.16(B)(1) through (B)(5), as applicable, shall be added together. No allowance shall be required for small fittings such as locknuts and bushings.
(1) Conductor Fill. Each conductor that originates outside the box and terminates or is spliced within the box shall be counted once, and each conductor that passes through the box without splice or termination shall be counted once. Each loop or coil of unbroken conductor not less than twice the minimum length required for free conductors in 300.14 shall be counted twice. The conductor fill shall be calculated using Table 314.16(B). A conductor, no part of which leaves the box, shall not be counted.
Exception: An equipment grounding conductor or conductors or not over four fixture wires smaller than 14 AWG, or both, shall be permitted to be omitted from the calculations where they enter a box from a domed luminaire or similar canopy and terminate within that box.

So, the light fixture you have in your post would qualify as a domed luminaire and the wires from the fixture itself can be omitted from the calculation if there are only 4 or less. However, this does not add volume to the box calculation itself.
Unfortunately, junction box overfill is probably the number one violation of the Code.
Good luck and stay safe!