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

out = ''
for t in range(int(input())):
    n = int(input())
    a = list(map(int,input().split()))
    mx = max(a)
    f=1
    for i in range(n):
        if(a[i]==mx):
            if((i-1>=0 and a[i-1]<a[i]) or (i+1<n and a[i+1]<a[i])):
                out+=str(i+1)
                f = 0
                break
    if f:
        out+=str(-1)
    out+='\n'
print(out) #C