Does anyone have recommendation for tilers in Klang Valley / PJ area?

Am doing a sub-sale home reno currently but having an issue with the main con (supposedly a reputable ID company) regarding the tiling works.
Their standard height for waterproofing at SHOWER area is 1 ft.
Their reasoning is that their tilers informed that if do 6ft waterproofing, the wall tiles may not stick so well and there's risk of hollow/popping tiles. Is this true?

Have tried discussing and trying to come to a resolution and I've suggested either :
1/ continue with their standard 1 ft water proofing but extend the general 1 yr warranty to 3 years warranty for water proofing (that's not too demanding, is it? I understand that most would provide >=5 yrs warranty on waterproofing
2/ do 6ft waterproofing and the general warranty for tiles hollow/popping remains at 1 year

They did not agree to either. If their 1ft water proofing has not been an issue, I don't see why they cant just provide me a 3 year warranty.
For the 6ft waterproofing option, they refuse to provide the 1 yr warranty on any SHOWER tiles that is hollow/popping.