The air resistance does not depend on the angle at which a spacecraft enters the atmosphere. The angle does determine how long a spacecraft is in the upper regions of the atmosphere where the air is much less dense. A spacecraft needs to be there long enough to loose most of it's speed.
The angle at which a spacecraft can approach the earth is called the re-entry corridor, see figure below. (Note that the figure is schematic, the atmosphere is only about 40 km thick, hardly a visible dot on this scale)
The re-entry corridor is a narrow region in space that are-entering vehicle must fly through. If the vehicle strays above the corridor, it may skip out.If it strays below the corridor, it may burn up and/experience excessive g-forces.
A spacecraft may skip out on purpose, this is called a skipped re-entry. The maneuver may also be used to loose speed to get a spacecraft in to an orbit. If a spacecraft skips out of the atmosphere again it will come back unless it has enough speed to escape the gravitational field.
The angle at which a spacecraft approaches a planet is called re-entry flight-path angle, γ, see figure below.
Flight path angle
At around 20 to 30 km altitude the density of the atmosphere starts to increase significantly:
Density vs Altitude from North Carolina Climate Office
The resistance in air is calculated as D=Cd*0.5*density*velocity^2. It is proportional to the density, and proportional to the velocity squared. At velocities in the order of several km/s, the drag is enormous when a spacecraft comes in to the denser atmosphere with high speed. To avoid high drag and therefore high g-forces and heating, a spacecraft needs to stay long in regions with a low densty so it has enough time to shed most of its speed there without high g-forces
If the flight path angle increases, the maximum g-forces and and heat input increase rapidly:
G-force during re-entry
Heating rate during re-entry
The maximum g-force a person can survive in good health is around 10g, therefore small flight path angles are usually chosen for manned re-entry.
All figures and part the explanation are from -FAA Advanced Aerospace Medicine On-line > Section III - Space Operations > Chapter 4 Basic Concepts of Manned Spacecraft Design > 4.1.7 Returning from Space: Re-entry:
FAA Advanced Aerospace Medicine On-line: