1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

t=int(input())
for _ in range(t):
    n=int(input())
    inp=list(map(int,input().split()))
    a=max(inp)
    b=min(inp)
    if a==b:
        print (-1)
        continue
    else:
        a=max(inp)
        for i in range(len(inp)):
            if inp[i]==a:
                if i+1<len(inp):
                    if inp[i+1]<a:
                        ans=i+1
                        break
                if i-1>=0:
                    if inp[i-1]<a:
                        ans=i+1
                        break
        print (ans)