Okay, how about to remove the LA floor, you need to both be on the same continent AND have either a direct land connection or have your capital in the same colonial region (the latter condition existing so that CNs in the Caribbean aren't horribly gimped). If both conditions are met, no LA floor (provided you don't have one for a different reason). Also, under this system, colonial nations lose their magic immunity to LA floors, since the other American continent is no longer a freebie
Asians might get Siberia or a single Pacific Island as a freebie with gamey tactics, but neither will amount to that much, since the unsettled portions of the islands that can be utilized like this are relatively small and Sibiria has crap for base tax no matter what you do. About the best they could do is the Philippines, which would add a little bit of taxes and manpower - at a quite steep ADM cost for moving the capital.
In the mean time, those nations that are on the least settled continents (the Americas (Oceania doesn't count as there are no nations that start on that "continent")) aren't gimped to half of what the colonial nations and ex-colonial nations get, as said CNs and ex-CNs get the full benefit of the most optimal method of expansion. The Americas are the region that I'm most concerned about here because a.) moreso than any other region, same-continent colonization is the only means of expansion or close to it, as there are far more uncolonized provinces in the Americas than on any other continent and b.) the region is unique in that it contains both nations that get LA floors on colonized provinces and ones with an immunity to this floor. For this method of expansion to have literally twice the returns on the same investment for one group (anyone who had the fortune of arriving from any other continent - including the other America) as for another (anyone who had the misfortune of being a native of that continent) is unfair, inconsistent, and encourages people to look for gamey strategies to bypass it (such as colonizing South America from North America to get the CN LA floor immunity). Hopefully, the rules I proposed at the top of this post satisfy a means for giving natives and CNs the same rules while not making same-continent colonization too OP on other continents.
And as for Africa, so what that same continent colonization is extremely optimal? No really, so freaking what? African nations aren't exactly known for being powerhouses and most of the land there is extremely hard to settle (tropical), and to eliminate the LA floor on the non-tropical parts, you'll need to colonize through the tropical parts, which until you advance enough technologically, isn't just a large investment, but literally impossible.