LED PCB uses minimal thermal copper pours on top layer ...why?

[treez]

Hello,
We have a 4 layer FR4 PCB which has power LEDs on it as in the attached. This PCB sits on a heatsink and so there are thermal vias down to bottom layer thermal copper pours.
The jpeg shows the top layer in red and bottom layer in blue. For some reason , our PCB layout engineer has used minimal area thermal copper pours on the top layer, probably because of all the tracking on the top layer. –Though why did he not just use a middle PCB layer for the tracking and make the top layer thermal copper pours larger?

 

[SLK001]

For some reason, our PCB layout engineer has used minimal area thermal copper pours on the top layer, probably because of all the tracking on the top layer.

Probably because you let him. If you're the design engineer, he should be taking direction from you.

...why did he not just use a middle PCB layer for the tracking and make the top layer thermal copper pours larger?

If he does this, there will have to be vias on all layers, which may, or may not interfer with mounting the board. Again, as the design engineer, if this can be done and it is what you want, then direct him to do it.

 

[treez]

If he does this, there will have to be vias on all layers, which may, or may not interfer with mounting the board.

Thanks, sorry i didnt provide full info.... i didnt show the edges of the baord where the control section is...here there are loads of through vias...therefore, having more in the LED area wont matter in this case.
Also, the thermal vias near the LEDs come out to the bottom layer, and all the bottom layer copper pours are "bare", with no solder resist over them.

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Aaaah, i see wht you mean SLK001, if he had put the tracking near the LEDs on the inner layers then the through vias would have "cut up" the bottom layer copper pours......thankyou