I've seen one study where 1% Polysorbate-20 improves penetration in-vitro 3x fold at what I assume is neutral pH in "Penetration Enhancing Effect of Polysorbate 20 and
80 on the In Vitro Percutaneous Absorption of L-Ascorbic
Seems like a sensible choice for a serum type formula with a a small 1-3% oil phase, it could emulsify Tocopherol and at the same time potentially improve penetration, or perhaps penetration at pH 3 is strong as is?
Another route could be to find a pH stable gelling agent with some emulsification capability, or explore other emulsifier such as Laureth-23. Thoughts?