Increasing a recipe's OG, should I increase dark malts too?

[kebabman]

I have a recipe for a porter that I would like to increase in OG by about 13% keeping the brew length the same.
Should I achieve the increase in OG by just increasing the amount of pale malt in the grist or should I increase all the malt including the brown, crystal and chocolate as well, keeping everything in the same ratio as the original recipe?
I am wondering whether increasing the dark malts will be too much or does the increase in OG need the dark malts increased to keep things balanced?
Any opinions very gratefully received, cheers

[dave-o]

Just increase the pale malt.

[kebabman]

Thanks Dave-0 for the confirmation, I suddenly had the thought that I was probably going wrong and was about to make the beer too roasted in taste.
Cheers

[dave-o]

Yeah, if you were increasing the size of the brew then increase all grains in proportion.

To just increase ABV and keep roughly the same taste, pale malt only (or sugar - perhaps a bit "ghetto" but would be absolutely fine in a dark, full-flavoured brew IMO).

[haz66]

+1 for the above, keep everything in the same ratio to achieve the same taste at a higher ABV