Mixing of requirements of different standards is not a good practice from formal as well as from technical point of view. Each standard requirement is a part of a complex system of interrelated requirements and rules which form the standard. You shouldnt take them individually without considering the whole.
In your case, if you draw RT procedure according to ASME V you should follow its rules in all respects, also in determining the number of exposures for circumferential welds. So, instead of referring to Fig. A.4 in EN 1435 you should use the clause T-271.2 of ASME V, Article 2. For example, for typical double-wall exposure, single-wall viewing technique (Exposure arrangement D), it requires a minimum 3 exposures taken 120 deg to each other.
Of course this is only a MINIMUM and you have to remember about all other rules of ASME Code. Specifically, in this case, you have to check if your RT technique ensures radiograph density limitations according to clause T-282.1. In some cases of heavy wall piping you may not be able to meet this requirement with only 3 exposures. You may find some help on the subject on my web site: http:\\www.ndtsoft.eu