Some of my plants have a fairly narrow pH range and some have a very wide range (see examples below).

Is it better to keep the pH the lower number, the high number or split the difference?

pH range Diff. Plant

6.1 to 6.5 0.40 Euphorbia milii (Crown-of-Thorns)

5.5 to 6.5 1.00 Camellia japonica 'Kramer's Supreme'

4.5 to 6.0 1.50 Azalea

5.6 to 7.5 1.90 Protasparagus densiflorus 'Meyeri'
(Foxtail Fern)

5.6 to 8.5 2.90 Tecoma capensis (Cape honeysuckle)

4.5 to 7.5 3.00 Prunus cerasifera (Purpleleaf Plum)

4.5 to 8.5 4.00 Lantana camara