What are your hair properties and dew points/ humidity? Might be your top layer is more damaged due to sunlight, brushing, shower beating down etc. Try washing and styling upside down for more volume and root wave, but it may be that is just the way your hair is.

Hydrolysed protein and magnesium sulphate can boost waves, additional leave in conditioner or styling product can smooth frizz. Lots of people seem to like flaxseed gel or okra gel.

Conditioner washing can shift greasiness if that is the route you go, conversely harsh shampoos can strip the scalp causing it to produce more sebum. For product build up simply avoid products and ingredients that b build up - silicones, waxes, some polyquats, butters.
2a-2c, medium texture, porous/ colour treated. Three years CG. Past bra strap length heading for waist.

CO-wash: Inecto coconut/ Elvive Volume Collagen
Treatments: Komaza Care Matani, coconut/ sweet almond/ fractionated coconut oils, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss Ultimate Volume, various Elvive
Styler: Umberto Giannini jelly, Au Naturale styling gelee
Flour sack towel, pixie diffuse or air dry.
Experimenting with: benign neglect