Hello Chen,
We did not carry out dedicated studies on how array pitch affects the heat dissipation.
However, the thermal losses are indeed influenced by the PV module support structure and it affects the convective cooling on the back plane. The advised U coefficients corresponding to each structure type are described here:
https://www.pvsyst.com/help/project-design/array-and-system-losses/array-thermal-losses/index.html#u-value-determination
It is also possible to measure the U coefficient values for your installation as explained here:
https://www.pvsyst.com/help/project-design/array-and-system-losses/array-thermal-losses/u-value-measurement.html