If you're worried about pH and still want more cranberry flavor, you could add more to secondary. Since you're planning on a melomel, you might want to consider 71B for your yeast, and target ~1.120 for your OG...that yeast should end you in the mid 1.0teens, and give you a little residual sweetness to temper the tartness of the cranberries, especially if you add more in secondary to get some additional flavor.
I agree w/ BBBF that I'd add some citrus zest...
Packaged: Red X Weimea SMaSH
Recent Meads: Mead Day '11 Ginger Metheglin, Mead Day '12 Traditional (orange blossom) Mead, Simple Cyser '12
Secondary: Why do I keep this line here...?
Bulk Aging: Cocobochet, Wild Cider, Simple Cyser
Planned: Hop Metheglin #3 (NZ hops), Trad. Gesho T'ej