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

for _ in range(int(input())):
    x=input()
    l=list(map(int,input().split()))
    if(len(l)==1):
        print(0)
    elif(len(set(l))==1):
        print(-1)
    else:
        m=0
        a=-1
        for j in range(len(l)):
            m=max(m,l[j])
            if(m==l[j]):
                if(j-1>=0 and l[j-1]<m):
                    a=j
                    break
                if(j+1<len(l) and l[j+1]<m):
                    a=j
                    break
        print(a)