Well you can only see a sunset that sets into the sea on the west coast, thats on the same time as san antonio. Any beach side location which faces west will give you sunset views although there are a few places which are more set up for this type of evening event, one of the places
is call kumharas which is situated around the bay just along from the hotel milord, its sort of a hippy type atmosphere where lots of people gather and not too commercial

http://www.kumharas.org/inicio.htm

On the other side of san antonio town there is an area known as the sunset strip, where you get bars such as sunsea, savahnna, cafe del mar and mambo, a litle further round in cala de moro there is the wonderful coastline. All of the bars face onto the sea and go through the ritual of the sunset experiene along with chill out music and after sunset performances of fire eaters etc.

http://www.ibiza-spotlight.com/night/cafe_del_mar_i.htm
http://www.cafemamboibiza.com/main.asp
http://www.sunseabar-ibiza.com/

here is map of the area where the sun set strip is
http://www.ibiza-spotlight.com/maps/w_i.htm next to number one on the map

With escana being on the north east coast, you will have to travel across to san antonio for the best sunsets, although if you get up early you should get some good sunrises over there

the sun sets around 8.30 ish from may onwards, however in july its a little later but the bars tend to get busy well before this time so if you need a seat get there by 7.30 at the latest although you can just on the rocks with a glass of wine and chill with the view

you will find a mix of all types of people at these place, young and old and of all nationalities particularly spanish.

I will be in san antonio in may and august so might see you there!!!
here is link to a webcam which overlooks the sea at the sunset strip next door to cafe del mar, it updates every ten seconds so you can check on the weather
http://www.zett-records.de/ibiza-sunset/ecard2.php?time=10&mez=MEZ&sun=7:60:18:14

Thanks for that Lukey

This is exactly the information I was looking for

Kumharas is a windmill and you can actually go to the top of it and watch the sunset from there. We stayed at the Costa sur in San an bay and it's about five minutes down the road (if you turn right out of the hotel) on the left hand side down a road that has trampolines at the top of it. Or you can sit on one of the many been bags and just chill. if you know what I mean!!!!!