My big sister and her partner ( the farmers ) live not far off the Tropic ( Capricorn ) in rural mid Queensland.
I emailed her ( asking about the tomato varieties they've grown successfully that handle tropical heat and extreme UV ). She recommends summer taste, scorpio, tracer, grosse lisse, futura and cherry varieties.
She grows her's in full sun .
Can I make suggestions regarding cooling the soil .
1) lay loose hay mulch over the soil ( will shade it and keep it cool and keep it moister , and will eventually break down and can improve the soil carbon and nitrogen contents and it's structure ) . My sister uses sugar cane straw mulch on all her bed ( is very cheap for her as she's got lots of sugar cane farms near her ,all she needs do is give a cane grower a call, and she wakes up next morning to find a load has been left for her ( often right next to her garden beds , best price = $0.50 , the price of a phone call ).
2) or modify the emissivity of bed top surface so it's more reflective in the IR range.
This is a recent study
Soil emissivity and reflectance spectra measurements
José A. Sobrino, Cristian Mattar, Pablo Pardo,Juan C. Jiménez-Muñoz, Simon J. Hook, Alice Baldridge, and Rafael Ibanez
APPLIED OPTICS / Vol. 48, No. 19 / July 2009
https://www.uv.es/ucg/articulos/2009/Publications_2009_5.pdf
and this
Estimating the broadband longwave emissivity of global bare soil from the MODIS shortwave albedo product
Jie Cheng, Shunlin Liang
Journal of Geophysical Research: Atmospheres JAN 2014
VOL119, p614–634
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2013JD020689
Northern winter soil emissivities
Northern summer soil emissivities
Can instantly modify the surface emissivity by applying a shallow layer of exfoliated vermiculite ( like many reptile breeders use to incubate their eggs ).
Has a low emissivity value e = 0.60 ==> it is very reflective in the IR region. [ r = 1- e ]
https://www.vermiculite.uz/index.php?l=en&s=teploprovodnost_vermikulita