1) By definition, heaven is situated in a higher place than the grave: Acts 1:9. True or false?
A - Acts 1:9 does not define either "heaven" or "the grave"
B - The actual definitions of "heaven" and "the grave" in the supernatural sense of those words do not specify any relative "height" (though one non-supernatural definition of "heaven" is "the sky")
C - Acts 1:9 does not teach us that heaven is above, at the same level, or lower than "the grave"
2) By definition, the Resurrection of Christ and his ascension into heaven implies that Jesus had moved from a LOWER POSITION in the grave to a much HIGHER POSITION in heaven:-
A - Nothing about "the grave" is mentioned in Acts 1:9.
B - The definition of "ascension" (a word not used in Acts 1:9) does suggest rising, but can refer to a physical change in location. Remember: all such references are RELATIVE, and in this case relative to the surface of the Earth. You could also argue that climbing a mountain means that you are at a much higher position than the bodies in the cemetery at the bottom of that mountain...but I would wonder why you would bother.
3) The above Scripture has described Jesus's ascension into heaven, which is a general movement from a LOWER POSITION in the grave to a much HIGHER POSITION in heaven.
That is NOT what "ascension" means.
Conclusion: careless (imprecise) wording and careless reasoning.