I'm glad I found this thread in time to change the bracing on my concert build in-progress
A few points to consider for anyone wanting to try this style of bracing and an elliptical bridge plate. None of these ideas are original, they have been gleaned from various sources.
If you use a wide spread and angle for the two fans, consider fashioning a 'belly buster' centre brace as future insurance should you get undesired bellying as the instrument ages. This is wise if you like paring down (scalloping) the braces finely. See footnote if you are unsure or curious. To be able to implement this, the central finger brace needs to 'step onto' the bridge by less than half the plate width, otherwise, the belly buster will have insufficient glued area to attach securely to the bridge plate.
Elliptical bridge plates gain one of their advantages by having less mass for a given length than their rectangular counterparts. Another advantage is that they present a single point at their ends and are less likely to contribute to soundboard grain line splitting. To utilise this feature they should be cut longer but not much wider than the bridge. I can think of no reason to make them any thicker than ~ 2mm (spruce).
FN: 'Belly buster' type braces are simply central accessory braces, usually used in the repair of steel stringed guitars where the centre bracing has sagged under high string tension. In this usage (for ukulele) it is used as insurance against the failure of overly light bracing, which while sounding lively, can't be guaranteed to not eventually belly-up excessively.
In an anticipatory role it can be precisely fashioned, but not installed, before the box is glued up. This makes retro-fitting through the sound hole relatively easy (but fiddly) using magnets for alignment. Be sure to mark the serial number of the instrument onto the brace for future identification.
If this sounds like a hassle, or too much effort for too little gain, use a narrower spread, or go with a three fan pattern.