Aussie climb gradients and obstacle height

[sru]

OS, John,

I have to stop thinking ....... One last question and I'll stop bugging you both I promise

Re the runway slope. I understand down slope is the most limiting, factoring this into the obstacle height, ( worst case 15000m, 1.6%, OH 787') is it valid to add the slope to the published gradient ( and reverse for up slope)? At 15000m 0.1% slope = 49'

Or is it more correct to add the height difference and leave the gradient the same for consistency?

Or are there other things I am missing (as I suspect!!). I know it can't be that simple.

Thanks

SRU