Very weird. I had read your sketch (probably because I knew what I was trying to achieve) as the third method. How I don't really know for certain. LolFirst one is as the lower part of your original picture - a 30mm radius on the end of the bar.
Second one is as my sketch - a 15mm radius on the two sides of the bar when it is sitting with 60mm horizontal and 15mm high (flat top with curved sides).
Third one is as Misterg's sketch - 60mm vertical, 15mm horizontal and a 7.5mm radius (semicircular in the 15mm direction).
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Just to really throw the cat amongst the pigeons, it would be possible to combine 1 & 2 above (option 4) or 1 & 3 above (option 5), but not 2 & 3.
This might be totally off track but the required shape looks a tiny bit (like in a dark room from far away) like 'convex feather edge bar' used for handrail tops (https://www.fhbrundle.co.uk/steel-sections/convex-bar?query=&sort_by=score&sort_asc=true). Maybe that could be considered as a possible alternative to the machined version.
But yes it seems like the 5/16 cutter I already have should do what I need. So I will delay buying a new cutter till I get time to try again.