when I install Ubuntu 16.04 with UEFI+ GPT, I feel uncertain! Why I don't select default install? Because it's stupid.
When I create a EFI partition, should I select primary or logic?
When I create a EXT4 partition, should I select primary or logic?
When I create a SWAP partition, should I select primary or logic?
And what's the function of "reserve boot area"?
Legacy BIOS has a limitation of 4 primary partitions and 2.2 TB per drive.
With UEFI, this limitation is now 128 primary partitions and 8 ZB (source: Wikipedia).
So you can choose either primary or logic partitions, UEFI will deal with them anyway. On my laptop, I have chosen primary partitions, it sounds proper than logic partitions on the same primary partition.
Regarding to your question about reserved boot area, the only topics I find on it are this one and this one, both quite old. But both give a similar answer, so I'd like to ask: are you 100% sure you boot in UEFI mode and not legacy mode?
It really doesn't matter, as UEFI has a very high partition limit and a logical partition is not really required. A logical partition is really a workaround for the legacy BIOS, which only allowed for 4 partitions on one drive. It essentially created a "master partition", which looked like one big partition to the BIOS, which would have many smaller partitions under it. However, as UEFI has a much higher limit at 128 partitions, unless you intend to create that many partitions, I suggest using primary so as to not add complexity to your installation.