Macro behind small domes

Ike has both 6" dome ports and flat ports for macro lenses. (In particular I've got the Oly/Zuiko 35mm macro for my E330...I intentionally went with it as a training-wheel macro since I've never owned a macro lens of any kind before, and read here that the stronger macros (50 or 105) took way more practice to get right).

I believe I understand the basic effects of flat or domed air/water interfaces: a dome will (or should, if placed right) preserve the range of a given lens, at the risk of needing a diopter for close focusing (not an issue for a macro but for wider lenses). A flat port actually magnifies but might vignette or lose ability to focus out at infinity. (Hopefully I'm right so far)

So, barring 'supermacro' where obviously the flat port is best for both getting really close and gaining some more magnification...is there really a lot of loss in using a 6" macro port for a weaker macro lens like a 35 - 50mm type range? Do you lose some range or is the loss simply because the dome is sticking out so you can't get quite as close as you could if it was flat?

I see ebay has a couple of the 5503 ports available and was thinking of bidding, since I'm slowly building up my kit scavenging, but then again there may be a REASON I see those ports for sale and not flat ones... My primary interest is still wider angle, and I suspect the 14-54 will be my primary diving lens, but I did get the macro to play around above water a bit and thought if I can get a port cheap, why not? Just don't want to waste even a little money if it's just a totally fubar idea.

I don't think there's much sacrifice optically, but it will be VERY easy to scratch a plastic dome port doing macro shots, especially with a relatively short lens.

In my experience, the potential benefits of using a dome with a macro lens are outweighed by the difficulty in getting a proper match between position of the len's nodal point and the dome's spherical center.

If I were you, I'd go with the flat port where you can get excellent results with a good quality macro lens, and the nodal point challenges become moot. A flat port is cheaper too.

Jerry