For those that wish to know... Cock height is useful to some no doubt, but there are some people I know that would require the basin to be head height for that use to be achieved.
Disabled basin heights 720-740mm to the rim.
Public and commercial buildings 780-800mm to the rim.
Average pedestal...
I'd stop wasting valuable time. CH System power flush with Sentinel X400. Save time and money. You've proven to have severe magnetite presence, so restriction on flow is there.
Whilst system is drained, fit yourself a magnaclean filter on.
Clean your CH top up tank, make sure there's a lid on...